This invention relates to radiation therapy of tissue surfaces as adjuvant or primary care for proliferative disease or other pathological conditions or as primary treatment. Discussion herein is largely directed to radiotherapy of exposed anatomical surfaces, e.g. skin, for treatment of proliferative disease, but it is to be understood that the apparatus and methods may be applied to different anatomical sites whether naturally occurring or as a result of surgical intervention, and for other therapeutic purposes.
It has been demonstrated in many areas of surgical oncology that adjuvant radiation treatment following tumor resection reduces the likelihood of recurrence of cancer or other proliferative disease. The likelihood of infiltrative disease decreases with distance from a primary site in a tissue with confirmed disease.
Commonly used traditional methods of radiation surface treatment would include positioning low energy radionuclide seeds in a pattern, often on a mesh substrate, in or on a surface to be treated. Because of the low energy levels and prolonged treatment times, these seeds are often left in the patient permanently.
Traditional methods would also include large, high-energy external radiation beams in the megavolt range. Such beams are often pencil-thin and are scanned from a range of perhaps 50 to 200 cm in order to carry out a prescribed treatment. If necessary, large elements of the apparatus, or even the patient, are manipulated in order to reduce exposure of normal tissue to unnecessary levels of radiation, and to still comply with the prescription.
Recently, it has been shown that relatively low energy, high dose rate radiotherapy delivered proximate to the treatment surface can be as effective as either low dose rate seed treatment or external beam therapy. It does not require seeds be left in the patient over long periods or permanently, nor does it risk exposing normal tissue to inadvertent radiation exposure. It is therefore desirable that such techniques be made available to as great a population of patients as possible.
It is well known that radiation intensity diminishes exponentially with either attenuation resulting from materials placed between the radiation source and target, or by distance from the source, or both. Radiotherapists have therefore found that it is generally desirable to spatially separate the radiation source from the tissues being treated, or to provide an attenuating material through which the radiation must pass before encountering tissue. This reduces the intensity ratio between the radiation incident on the tissue surface and that at depth, minimizing the likelihood of over-exposing that tissue nearest the radiation source, while still delivering adequate radiation at the specified depth for effective treatment.
Early development in the application of relatively low-energy, high dose rate therapy involved development of applicators comprising relatively heavy sheets having a plurality of parallel source guides for use with radionuclide sources. These sources are often of iridium 192 positioned on wires, which are manipulated within source guides to deliver a prescribed treatment to the target tissue underlying the applicator. These surface applicators have several disadvantages, however. Their source guides have fixed spacing which may or may not be conducive to an optimal treatment plan, and further, the discrete spacing of the source guides within the applicator may contribute to non-uniformity in the delivered radiation dose. Still further, the applicator may have structural characteristics limiting its ability to conform adequately to the surface being treated without interfering with ease of source manipulation within the source guides. The so-called H.A.M. or flap applicators are representative of this sort of applicator. (Such applicators are available from Mick Radio-Nuclear Instruments, Inc., Mount Vernon, N.Y. 10550, or Nucletron, Columbia, Md.) It is an object of this invention to overcome these and other difficulties.
Emissions from iridium and other common medical isotopes usually have high-energy components which can penetrate deeply into tissue. They also emit continuously, and thus, like external-beam sources, can only be used in special, heavily-shielded rooms. In addition, concerns for the safety of personnel require isolation of the patient during treatment, shielded storage of the sources at all other times, and automated handling between the storage chamber and the applicator during patient treatment. Because of these considerations, the substantial capital expense required for such facilities dictates that treatment centers be located in urban areas so as to serve sizeable patient populations. This can result in under-serving rural patients who cannot repeatedly travel to urban treatment centers for a course of prolonged radiation treatment. Furthermore, the need for patient isolation is inconvenient for therapists, not to mention daunting for patients under treatment. Because of these limitations, it is clear that any improvements in total duration of treatment, cost, source handling and shielding requirements, patient fear factors and inconvenience would be welcome.
More recently, miniature electronic x-ray tubes have provided an alternative to use of radionuclides. Such tubes do not emit continuously; they only emit when powered in a manner causing emission and they can be turned on and off, or if desired, modulated such that their penetration depth can be controlled (by control of acceleration voltage) and their dose intensity can be controlled (by beam current) as well. One reference describing the principles and construction of such tubes is Atoms, Radiation and Radiation Protection, Second Edition, John E. Turner, Ph.D., CHP, 1995, John Wiley & Sons, Section 2.10. Electronic sources generally require provision for cooling, but otherwise are more versatile and convenient to use than radionuclides. They can be engineered to accommodate a wide variety of dosimetric prescription detail. Miniature x-ray tubes can be designed to emit substantially isotropically, or to emit only through a predetermined solid angle, perhaps permitting more spatially-detailed courses of treatment. Radionuclides cannot be controlled in this manner as easily. Furthermore, the x-ray energy spectrum in ranges suitable for use in this invention eliminates the need for heavily shielded structures, or “bunkers”, and also permits the therapist to be in the room with the patient during therapy. Therapy can proceed in almost any medical facility, urban, rural or even mobile, and therefore, with miniature x-ray tubes, a greater population of patients can be treated, and the costs of therapy are greatly reduced. It is clear that electronic sources have already contributed significantly to making such therapy as described above more readily available and cost effective than other methods. Although the apparatus and methods of this invention may be compatible with either radionuclide or x-ray sources, it is clear that electronic x-ray sources offer many advantages as outlined above. It is a purpose of this invention to further develop those advantages.
Other objectives of the invention will become apparent from the following summary, drawings and description.